Britain is responsible for two per cent of the global emissions of carbon dioxide for which human beings are to blame. Between now and 2010, the government aims to cut this figure by about a sixth. So, if this target is achieved (and things have not been going too well of late), the amount of man-made carbon dioxide going into the atmosphere will be reduced by just one third of one per cent. To save the planet from global warming, a 60 per cent reduction is thought to be required.

Our futile gesture will require the poor (though not, apparently, the rich) to be denied opportunities to travel. Our coasts and national parks are to be defiled by throbbing turbines, which will chew up migrating birds. Enormous sums that could alleviate human suffering will be expended instead on developing inefficient forms of energy generation. Why?

Even the most fanatical of our eco-puritans acknowledge that Britain alone cannot save the planet from global warming. They recognise that if our future depends on the scale of man-made carbon emissions, it is the behaviour of those more multitudinous and carbon-greedy than ourselves that will have to change. Our mission, as they see it, is therefore to set an example. We must show those lesser breeds that inhabit distant continents what they must do.

The imperial grandeur of this endeavour is inspiring. Cecil Rhodes and Lord Palmerston might have considered it over-ambitious. Unfortunately, of course, they would have been right.

Will the Chinese stop building a new coal-fired power station every week because Britain has increased airport tax? Will Texans abandon their car-dependent suburban lifestyles because more Limeys are insulating their lofts? Will the poor of Africa and Latin America abandon their aspirations for a higher standard of living because Ken Livingstone has raised the congestion charge for Chelsea tractors?

Parading our sanctimony might prove less effective than a whiff of grapeshot. Suppose that the British and other peoples currently wolfing more than our fair share of fossil fuels chose to make it clear that we intended to plunder them even more extravagantly. By bringing the spectre of disaster closer, we might shock the eager-to-become-equally-profligate into a readier appreciation of their own impending doom.

After all, they have more to lose than we do. As things stand, the world seems to be on course for a temperature rise of around 3°C over the rest of this century. The Earth was three degrees warmer three million years ago, and this entailed a sea-level 80 feet higher than it is now. The return of such a sea-level would be bad news for London, Liverpool and Hull, but Britain has high ground and plenty of money. Over a century, we could probably relocate the people and activities that would be affected. China, however, would find itself with 250 million displaced people to accommodate and most of its glittering new citadels under the waves. India would have 150 million homeless people to handle.

So, might this prospect make the developing world think twice about following us down the carbon-paved primrose path, and to push instead for collective carbon continence? In fact, of course, scare tactics would prove hardly more effective than pious example. The Chinese already understand what global warming entails perfectly well. Nowadays, even Middle Americans seem to have got the hang of it. The trouble is that this understanding does not change their behaviour, for reasons that will remain unaffected by any lesson that the British or anyone else may try to teach them.

Those American SUV drivers who accept that climate change is occurring believe it would remain unaffected by anything they might do. And of course, each of them, individually, is entirely right. Nobody can make a difference, for the actions of an individual do not determine collective behaviour.

An uncoerced group cannot be expected to act in what may be the group's best interests if the interests of individual members conflict with those of the group. The currently widespread refusal to acknowledge that this is so is an example of the fallacy of division. This fallacy is surprisingly common. In the 1970s, for example, it led politicians to assume, vainly, that workers would accept pay restraint because rising inflation operated against their collective interest.

Just as individuals are aware that acting in the general interest may not be in their own interest, so are governments. China's rulers know that the stability of their country depends on the continuance of economic growth. This will depend for the foreseeable future on the ever more vigorous exploitation of fossil fuels. In due course, calamity may or may not ensue, but that is a matter for another day. It will certainly not prevent today's individual decision-makers from enjoying the benefits of their anti-social behaviour.

Mercifully, this feature of human conduct seems likely to ensure that the example of carbon piety which our own government is intent on conveying to the world is unlikely to end up causing us too much inconvenience. Windmills may sprout atop our moorlands, but road-building will continue. The expansion of Heathrow and Stansted will go ahead unquestioned: the Prime Minister has explained that curbing air travel might cost votes.

Even the leading lights of our environmental movement cannot help inadvertently under-scoring what really is, for them, an inconvenient truth. They all doubtless buy low-energy light bulbs, but they seem to take to the air just as often as anyone else. In his new book, Heat, George Monbiot notes despairingly that one of his environmentalist friends holidays in the Pacific. "She doesn't get there by bicycle," he snarls. Unfortunately, however developed the lady's eco-awareness may be, she knows, like the rest of us, that her own behaviour will make no difference.

In fact, the current fad for ostentatious environmental self-righteousness, as evidenced by the windmill on David Cameron's roof, is, for the most part, no more than self-indulgent one-upmanship intended to bestow a feeling of moral superiority on its exponents. When it comes to action that might actually hurt its author, fine principles quickly go by the wayside. Cameron's bike is chaperoned by his Lexus; Coldplay warble about planet abuse but travel by private jet.

How could it be otherwise? Unlike ants, we are a species more or less incapable of adopting a common course of action that is at odds with the appetites of its members. We can make sacrifices for our families and sometimes for tribes or factions with which we have chosen to identify, but the brotherhood of man has never really caught on. Idealists blame this regrettable state of affairs on the absence of a world government, but in fact that absence is itself a consequence of the very phenomenon they lament.

Unfortunately, however, we are far more sensitive than ants to variations in our environmental circumstances. This vulnerability combines unhappily with a far greater capacity to inflict change on those circumstances than most other species enjoy. Unsurprisingly, the lifespan of the human race therefore looks likely to be short. Sooner or later, ants, which were here long before us, seem likely to see us off.

Ensconced irremovably in the last-chance saloon, we seem fated to reject the eponymous opportunity that it tantalisingly holds out. So, if we have indeed been bought our final drink, how ought we to conduct ourselves while sipping it?

Are we to spend our last moments clutching at straws, sermonising and pointing sanctimonious fingers at those whose part in our downfall is only slightly greater than our own? Surely our species' magnificent, if reckless, Promethean story deserves a more dignified and entertaining finale. If this entails a last grand orgy of fossil fuel consumption, well, so what?

Our sojourn on this planet may turn out to have been comparatively brief, but it was fun while it lasted. If it must now come to an end, as all things do, let's go out with a bang, and not a self-deluding whimper.

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